Can the use of iphone external lens significantly improve iPhone's photographic ability? Which brand of external lens is good?

In fact, even the most advanced lens can't reach the transmittance of 100%. Failure to reach the transmittance of 100% means that the definition will decrease. If you mean a filter the size of a fingernail, it will reduce the image quality to some extent, but it can bring some special effects (such as star glare, macro, fisheye, etc.). Therefore, whether you want the effect (style) or the image quality depends on your personal preference.

As for the brand, there is not much difference. After all, there is no leading brand of "mobile phone camera filter" until now, and there is no technical threshold for producing these filters. Anyone can produce it as long as the mold is opened. So if you want to buy it, it is recommended to look at shops with higher sales and better evaluation, such as Taobao.